The day before the summer solstice (as I wrote last month), two friends and I played 101 holes, all on foot. I took 59,255 steps, covered 28.6 miles and climbed the equivalent of 272 flights of stairs--and I know all of this because I wore a device called a Fitbit Ultra ($100, fitbit.com), which monitored my exertions.

A Fitbit is a thumb-size gizmo that you attach to your clothing or carry in your pocket. (The company's website says that women often clip it to their bra--a potential health-club conversation starter.) It contains an accelerometer, which measures your motion (and tracks your sleep quality, if you wear your Fitbit in bed); an altimeter, which counts floors climbed (and isn't fooled by elevators); a teensy computer, which estimates the number of calories you've burned and awards you an "active score" based on its assessment of your efforts in all categories; and a wireless transmitter, which uploads your data to your page on the company's website each time you come within 15 feet of your "base station," which is also a charger.

Because of my Fitbit, I now know that when I play 18 holes on my home course I walk between 5.5 miles (if I'm playing well) and 6.3 miles (if I'm spraying my drives), and that my favorite morning circuit with my dog is a little more than 2.7 miles. Of course, I was playing golf and walking my dog before I bought my Fitbit, so tracking those things didn't turn me into a better person. But quantifying even ordinary activities can inspire you to get off the couch, especially if you like to compete against people who are easy to beat, such as yourself. The website awards dumb but oddly inspirational symbolic "badges" for passing various thresholds, like doing the equivalent of climbing to the top of the Eiffel Tower. (I've taken my dog on bonus walks after noticing I was close to earning a new badge.)

Nike makes a competing device, called the Nike+ FuelBand ($150, store.nike.com). It goes around your wrist, like a bangle, and it measures most of the things a Fitbit does--although it doesn't have an altimeter, and you can't subdivide a day into separate activities (front nine, back nine) or use it as a stopwatch. Somewhat confusingly, it converts your results into an imaginary, opposite-world substance called Nike Fuel. (The more actual fuel your body burns, the more Nike Fuel you accumulate. What?) I find my FuelBand awkward to wear during golf because it's a thick, inflexible ring, which moves slightly when I swing. It also alternately overcounts and undercounts my steps, sometimes by as much as 50 percent, and gives me credit for walking when I'm doing things like driving my car or sitting in front of my computer.

During a recent round with my regular Sunday-morning gang, I wore both my Fitbit and my FuelBand, plus a control device: my wife's Omron HJ-113, a no-frills pedometer (omronhealthcare.com; $25 on Amazon). The Fitbit and the Omron agreed closely on steps taken--they were within about 1 percent of each other, both overall and during short test segments--but the FuelBand was off by a good 25 percent. An unexpected finding: Because the Omron attaches to your clothes but isn't tiny, it's less likely to take an accidental trip through the washing machine (a constant danger with the Fitbit) or into the shower (ditto with the FuelBand). Why aren't all sports gadgets waterproof?

EVERY LITTLE STEP
People sometimes say a good way to get healthier and slimmer is to walk or run 10,000 steps a day. That number (which for most of us equals about five miles) doesn't necessarily have a basis in anything a scientist would recognize as science. And, the seemingly obvious connection between exercising more and weighing less isn't straightforward, as Gary Taubes explains in his terrific book Why We Get Fat. Yet no one doubts that getting off your butt is good for you, and most of us don't do it enough.